Analysing private market research data, we estimate the degree of market concentration across 481 industries in the Australian economy. On average, the largest four firms control 36 per cent of the market. Some industries are considerably more concentrated. In department stores, newspapers, banking, health insurance, supermarkets, domestic airlines, Internet service providers, baby food and beer, the biggest four firms control more than 80 per cent of the market. We suggest ways in which high market concentration may increase inequality and discuss some policy ideas to address the problem.